Thermoplastic cellulose derivatives

Extrusion method to be used for thermoplastic cellulose derivatives)... 

Cellulose ester powders in the presence of different plasticizers and additives are extruded to produce various grades of commercial cellulose plastics in pelletized form. The nanoscale fillers can be mixed with these thermoplastic cellulose derivatives with the aid of plasticizers. Recently, Park et al. (2004) successfully used melt intercalation technique for the fabrication of cellulose nanocomposites fi om cellulose acetate (CA), triethylcitrate (TEC, as plasticizers), and organically modified clay. 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

Oridation. This is caused by contact with oxidising acids, exposure to u-v, prolonged application of excessive heat, or exposure to weathering. It results in a deterioration of mechanical properties (embrittlement and possibly stress cracking), increase in power factor, and loss of clarity. It affects most thermoplastics to varying degrees, in particular polyolefins, PVC, nylons, and cellulose derivatives. 

Wise and Rocchio [32] have discussed the processing techniques for LOVA formulations which invariably depend on the type of binder. The polybutadiene-based formulations referred to as cured systems, are processed through a solventless process whereas formulations based on cellulose derivatives and thermoplastic elastomers as binders are processed by a solvent process similar to standard NC propellants. In conclusion, LOVA formulations offer unique propulsion systems for tanks with the potential to offer high energy and low vulnerability. 

Among the various types of cellulose derivatives, it is the cellulose esters that find the widest practical application and complete succesfully in a number of branches of the industry with synthetic polymers. The complete or partial esterification of the hydroxyl groups of cdlulose can yield cellulosic materials having such technically valuable properties as thermoplasticity, hydrophobicity, resistance to heat and light, stability to the action of putrefying microorganisms, bactericidal action, etc. 

Lacquer. A coating composition that is based on synthetic thermoplastic film-forming material dissolved in organic solvent that dries primarily by solvent evaporation. Ts pical lacquers include those based on nitrocellulose, other cellulose derivatives, vinyl resins, acrylic resins, and the like. 

Thermoplast . [BASF BASF AG] Dyes for mass dydng of thermoplastic arid thomosetting plastics, cellulose derivs. 

Cellulose derivatives were the first thermoplastics formed in the film blowing process in the beginning of the 20th century. By the 1930 s, biaxially oriented films of cellulose acetate were commercially available. Forming of synthetic high polymers, especially LDPE, by the film blowing process began only in the 1940 s. 

Natural polymers unlike the S5mthetic ones do possess very complex structure. Natural polymers such as cellulose, wool, and natural rubber are used in many products in large proportions. Cellulose derivatives are one of the most versatile groups of regenerated materials with various fields of application. Cellulose is found in nature in all forms of plant life, particularly in wood and cotton. The purest form of cellulose is obtained from the seed hairs of the cotton plant that contains up to 95% cellulose. The first cellulose derivatives came to the stage around 1845 when the nitration of starch and paper led to discovery of cellulose nitrate. In 1865, for the first time, a moldable thermoplastic made of cellulose nitrate and castor oil. 

Synthetic thermoplastics which soften on heating, e.g., cellulose derivatives, vinyl polymers, saturated polyesters, polyacrylates, polyethers, and polysulphones. 

Cellulose represents an important polymer, which is most abundant in nature, and serves as a renewable resource in many applications, e.g., fibers, films, paper, and as a composite with other polysaccharides and lignin in wood. Cellulose derivatives will also be used as films and fibers, food additives, thermoplastics, and construction materials, to name just a few. Cellulose and cellulose derivatives have played an important role in the development of the macromolecular concept. So far, little use has been made of the fact that cellulose represents a chiral material except, e.g., in a rare case as stationary material in liquid chromatography for the separation of chiral compounds. Nature ifself uses the chirality of cellulose occasionally, and twisted structures of cellulose molecules are found in cell walls. 

The cellulose ethers constitute another important group of cellulose derivatives prepared from alkali cellulose by standard etherification reactions between the hydroxyl groups and an alkyl halide. The properties of the ethers depend on the extent of the reaction that is, the degree of etherification. In general, the ethyl celluloses are water-insoluble thermoplastic materials, whereas methyl ether, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose are soluble in cold water and are used as viscoelastic thickeners and adhesives. 

Cyclic anhydrides like acetic, phthalic, and succinic anhydride have been widely used in cellulose modifications to produce different cellulose derivatives such as cellulose acetate, cellulose butyrate, cellulose benzoate, cellulose phthalate, and cellulose with or without catalyst, which have several applications such as water absorbents for soil in agriculture, drug delivery system, and as thermoplastic. 

Thermoplastic starch and cellulose derivative systems have been also reported [98,111,118, 119], particularly with cellulose acetate and butyrate in presence of glycerine and epoxidized soybean oil [118],... 

This chapter first gives an overview of cellulose raw materials and their molecular and supermolecular structures. The principles of shaping cellulose into fibres, films, and nonwovens by means of solution techniques are then outlined followed by a section on properties and market applications of these materials. Derivatives of cellulose are presented with special emphasis on thermoplastic cellulose esters, typical plasticizers, and promising reinforcing materials. Finally, recent developments and future prospects of cellulose materials are reviewed as far as the above applications are concerned. This book does not cover the important applications of cellulose and ligno cellulose fibres for reinforcing thermoplastics, like wood plastic composites (WPC) and natural fibre reinforced plastics (NFRP), since in these cases cellulose does not substitute a thermoplastic. 

The most important group of cellulose derivatives for thermoplastics application and the only one used commercially in this field is cellulose esters. Apart from camphor plasticized cellulose nitrate as the first thermoplastic (celluloid), acetate, propionate or butyrate, are the most common hydroxyl group substituents, as shown in Figure 3.5. 

In this discussion we deal with the resistance of polymers to various chemicals, (mainly water, acids, bases or organic solvents) as well as with their endurance after being exposed to climatic conditions or to fire. Most polymers show very low water absorbency, except for Nylon and cellulose derivatives that are sensitive to humidity. Most polymers also withstand mild inorganic chemicals at ambient temperatures. Excelling at this are the fluoro compoimds, Noryl, polyimide and polysulfone while polypropylene, PVC and epoxy are considered fair. Polyester and polycarbonate are sensitive to bases, while Nylon is affected by acids. Detailed tables of data exist, describing the resistance of plastics to many chemicals at specific temperatures. Most thermoplastics have a tendency to dissolve in specific organic solvents. 

We already mentioned in Section 3.5 [70] the partial oxypropylation of cellulose fibres and the interest of the ensuing composite materials in which the unmodified fibre cores represent the reinforcing elements and their thermoplastic sleeves the source of a matrix. Other interesting approaches have been recently put forward to prepare composite materials in which cellulose or one of its derivatives prepared in situ are the only component. Glasser was the first to tackle this problem through the combination of cellulose esters and fibres by two distinct approaches, viz. (i) the incorporation of lyocell fibres into a cellulose acetate matrix [92] and (ii) the partial esterification of wood pulp fibres with -hexanoic anhydride in an organic medium [93] that produced thermally deformable materials in which the thermoplastic cellulose ester constituted the matrix and the unmodified fibres the reinforcing elements. 

Cellulose derivatives are additive components for many thermoplastic and thermosetting coating systems. Cellulose esters as film formers provide fast drying and early hardness development, flooding and floating suppression, and crosslinking reactions. 

The main applications of cellulose are timber, furniture and fuel textiles such as cotton paper, membranes, and explosives. Important cellulose derivatives are cellulose acetate and cellulose acetate but)n ate (thermoplastic esters) ethyl, hydroxyethyl and hydrox) propyl cellulose. 

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